1. Field of the Invention
The present invention relates to a process for the preparation of stable aqueous solutions of zirconium chelates at 100% chemical yield without effluent or solid waste. The aqueous zirconium chelate solutions remain stable upon aging, boiling, or dilution and also after the addition of acids and/or bases.
2. Description of the Related Art
Chelates are utilized in the paper coating industry as starch and protein insolubilizers and in the petroleum industry for fracturing petroleum bearing formations. Chelates are used in both aqueous and non-aqueous solutions to retain metals in solution at high temperatures and over wide pH ranges so that the metals remain compatible with other chemicals. Chelates can be formed of transition metals such as titanium, zirconium, copper, iron, and the like and also aluminum and boron.
Particularly in the petroleum industry, chelates are employed in cross-linking gels such those disclosed by Almond in U.S. Pat. No. 4,477,360. Almond discloses an aqueous gel containing a retarded cross-linking composition of a zirconium salt or chelate and polyhydroxyl containing compounds. Almond further discloses that the polyhydroxyl containing compounds be admixed with an aqueous fluid and a cross-linking compound featuring zirconium chelates. These compositions are typically referred to as polyols, examples of which include glycerol, erythritol, threitol, and ribitol. The gelling agents employed by Almond include guar gum, locust bean gum, karaya gum, sodium carboxymethylguar and several other compounds of guar.
Smeltz, U.S. Pat. No. 4,958,038 issued Sep. 18, 1990, discloses a process which comprises combining glycerol, erythritol, arabitol, etc. and lactic acid, glycolic acid, malic acid, citric acid, tartaric acid, saccharic acid, gluconic acid, glyceric acid or mandelic acid to provide an aqueous solution of polyol and alpha-hydroxy carboxylic acid, and then at an alkaline pH of 10 or less reacting the solution with a titanium compound of an inorganic acid at an alpha-hydroxy carboxylic acid to titanium mol ratio between 0.5 to 1 and about 4 to 1 and a polyol to titanium mol ratio between about 0.25 to 1 and about 2 to 1. In fracturing formations, Smeltz uses solvatable polysaccharides which include guar gum and locust bean gum, as well as other galactomannan and glucomannam gums, such as those derived from sennas, Brazilwood, Tera, Honey locust, Karaya gum and the like.
Hanlon, et. al., U.S. Pat. No. 4,460,751 describes a crosslinker which is made by preparing an alpha-hydroxy carboxylic acid solution, then adding a zirconium compound, e.g. zirconium oxychloride to form a second mixture, and finally adds the amine compound to the mixture. If zirconium carbonate is used, the zirconium carbonate is added to water to form a first mixture, next the amine compounded is added to form a second mixture, and finally the alpha-hydroxy carboxylic acid is added to the second mixture.
Examples of the previous nonadvantageous methods of preparing zirconium chelates involves the use of dangerous solvents, such as ethers and alcohols, for producing zirconium triethanolamine chelates via zirconium n-propyl or n-butyl zirconate solubilized in n-propanol. This method involves the soluablization of zirconium tetrachloride which is also a dangerous chemical in n-propanol or ether followed by reacting it with triethanolamine. See Kucera, U.S. Pat. No. 4,692,254 describing such methods in detail.
Also aqueous chelates are produced through the separation of insoluble chelates as intermediates such as zirconium citrate, zirconium lactate and zirconium tartrate. This process generates effluents such as sodium sulphate, ammonium sulphate and other anions such as chlorides, nitrates, etc. See Van Mater, U.S. Pat. No. 2,498,514 describing such methods in more detail.
The prior methods of preparing zirconium chelates for preparation of solutions useful in fracturing oil and gas strata have encountered such problems as low chemical yield, a need for an organic solvent which causes fire hazard and may produce toxic fumes or exhibits poor stability on aging and/or dilution, exposure to the atmospheric condition, dilution with water, boiling and/or the addition of inorganic acids or bases. Also, such prior preparation methods have generated organic and/or inorganic effluent and/or solid waste.